A microspeaker is provided in a portable device, etc. to generate sound. With recent developments of mobile devices, the microspeaker has been used for various devices. In particular, the latest mobile device tends to have a light weight, small size, and slim shape to facilitate portability, and accordingly, the microspeaker mounted in the mobile device is required to have a small size and slim shape.
However, in the case of a microspeaker having a small size and slim shape, an area of a diaphragm decreases, and a size of a resonance space in which the sound generated by vibration of the diaphragm is resonated and amplified also decreases, as a result of which a sound pressure level (SPL) decreases. Such decrease in the sound pressure level is particularly pronounced at low frequencies. There has been developed a technology of improving a low frequency sound pressure level, by arranging an air adsorbent in a resonance space, so that the air adsorbent adsorbs air molecules and defines a virtual acoustic space, to enhance a low frequency sound pressure level.
EP 2 424 270 B1 discloses arranging a zeolite material in a resonance space as an adsorbent, wherein a mass ratio of silicon composing zeolite particles to aluminum is at least 200.
In addition, U.S. Pat. No. 8,687,836 B2 discloses adopting silicon-based zeolite, which contains a small amount of second metal on a silicon basis, as an air adsorbent material in an enclosure, wherein a mass ratio of silicon to the second metal is equal to or less than 200.
EP 2 424 270 B1 discloses arranging a zeolite material in a resonance space as an adsorbent, wherein a mass ratio of silicon composing zeolite particles to aluminum is at least 200.
However, the technologies disclosed in EP 2 424 270 B1 and U.S. Pat. No. 8,687,836 B2 do not consider that, when the adsorbent is arranged in the resonance space to define the virtual acoustic space, the actual resonance space decreases as much as the space occupied by the adsorbent.